docs: def get_ras(repi, theta, mag, coeff):
      """
      Computes equivalent distance
  
      :param repi:
          Epicentral distance
      :param theta:
          Azimuth value
      :param mag:
          Magnitude
      :param coeff:
          GMPE coefficients
      """
      rx = 100.
      ras = 200.
      #
      # calculate the difference between epicentral distances
      dff = fnc(ras, repi, theta, mag, coeff)
      while abs(dff) > 1e-3:
          # update the value of distance computed
          if dff > 0.:
              ras = ras - rx
          else:
              ras = ras + rx
          dff = fnc(ras, repi, theta, mag, coeff)
          rx = rx / 2.
          if rx < 1e-3:
              break
      return ras